The present invention relates to landfill operation and to bioreactors. In particular, the present invention relates to an aerobically operated landfill. The present application claims the benefit of the priority date of provisional application serial No. 60/030,792, filed Nov. 14, 1996.
Aerobic decomposition of wastes is well known. Composting, for example, has been practiced in agriculture for centuries. However, most modern landfills are operated in an aerobic manner because of regulatory requirements. Nonetheless, there are advantages to aerobic decomposition of the types of wastes that are found in landfills and, accordingly, considerable investigation and interest exists in this art.
For example, in lysimeter tests conducted by the University of South Florida, it was shown that degradation of municipal solid wastes (MSW) can be enhanced by the application of water, the recycling of leachate, and the addition of air. Employing these processes on shredded MSW in a vertical lysimeter, waste settlement rates of greater than 25% were observed within 60 days. In addition, these tests showed significant improvement in leachate quality based on biochemical oxygen demand (BOD) and volatile solids. In light of this work and other MSW treatment studies, it is estimated that landfills that have at least a 50% organic fraction of waste, could achieve a MSW settlement of a least 15% by volume.
Although there are advantages to aerobic decomposition of wastes and keen interest in this art, methods for the demonstrated safe operation of landfills in an aerobic manner or for the cost-effective conversion of landfills from anaerobic to aerobic operation are not known prior to the present invention.
The present invention, briefly described, is an improved aerobic landfill, perhaps by converting an anaerobic landfill. The present invention increases the rate of waste stabilization, decreases the rate of production of methane gas, reduces the levels of toxic organics, and decreases the volume of leachate. As a result, the present invention presents a significantly reduced threat to the environment and a significant reduction in the cost associated with operation, closure, and post-closure of the landfill. The effectiveness of the aerobic landfill is based on applying the correct balance of air and recirculated leachate to the waste in the landfill. The recirculation of leachate provides, not only an ample supply of moisture, but sufficient oxygen, food and nutrients for organisms in the waste mass. Additional nutrients, such as those from sewer sludge or nitrogen, are not necessarily required for this process to operate.
The present invention also uses a combination of air injection through vertical wells inserted into the waste mass and horizontal leachate collection system piping. This combination allows flexibility in the application of air and leachate to the proper proportions to achieve a safe waste mass temperature preferably between approximately 120xc2x0 F. and approximately 140xc2x0 F. and most preferably close to 135xc2x0 F. Maintaining temperatures below 150xc2x0 F. is essential to preclude killing the microorganisms needed for the landfill to operate aerobically.
The present invention includes a unique system of degrading municipal solid waste (MSW) within a landfill by converting an existing anaerobic landfill to aerobic degradation in the following manner: (1) use of the landfill leachate collection system to inject air (2) vertical air injection wells installed within the waste mass; (3) a pressurized drip irrigation system for dripping leachate; (4) landfill gas vents; and (5) control systems for balancing air injection and recirculated leachate.
The primary goals of this invention are to stabilize waste and to reduce landfill operating costs and liabilities. After the waste is stabilized and rendered harmless, the landfill may be covered and redeveloped for other uses, or re-used.
Aerobically decomposing the waste in-place stabilizes the waste mass more quickly, reduces toxic organics in the leachate, reduces methane gas production, and decreases the volume occupied by the waste. Aerobic decomposition of the waste is accomplished by an engineered system referred to as an xe2x80x9caerobic landfill bioreactorxe2x80x9d or ALB. The ALB achieves optimal aerobic degradation of organic matter at safe waste mass temperatures and minimizes exposure of leachate or waste mass to human health and the environment. The present invention is confirmed by data collected during actual field applications performed by the inventors. An aerobic landfill bioreactor (ALB) system was installed and operated by the inventors at an active landfill in Grovetown, Georgia. This ALB system demonstrated over a nine month period that municipal sanitary landfills can cost-effectively be converted from anaerobic to aerobic degradation processes. It was proven through actual experience that the injection of air into the waste mass combined with the recirculation of leachate aerobically degrades MSW while waste mass temperatures remain stable between 120 degrees F. and 140 degrees F. This process, in turn, increases the rate of waste stabilization, decreases the production of methane, reduces the level of toxic organics, and decreases the production of leachate.
Those familiar with landfill operation will understand from a careful reading of the Detailed Description of Preferred Embodiments that many other features and advantages are in the present invention.